Air Pollution in Indian Cities — Explained

On this page

1. Understanding Air Pollution in Indian Cities: A Vyyuha Analysis
2. Key Legal Frameworks:
3. Authoritative References:

Detailed Explanation

Understanding [LINK:/environment/env-08-01-air-pollution-in-indian-cities|Air Pollution in Indian Cities]: A Vyyuha Analysis

Air pollution in Indian cities has emerged as one of the most pressing environmental and public health challenges of the 21st century. The rapid urbanization, industrialization, and population growth have led to a complex cocktail of pollutants, often exceeding national and international safety standards. From a UPSC perspective, the critical examination angle focuses on the multifaceted causes, severe impacts, and the efficacy of multi-level governance responses.

1. Origin and Historical Context

Historically, air pollution was localized, primarily linked to natural sources like forest fires or volcanic eruptions, and later to rudimentary human activities such as burning wood for cooking and heating.

The pre-industrial baseline in India, like much of the world, featured relatively clean air. However, the advent of the Industrial Revolution in the West, and its subsequent spread to India, marked a significant shift.

Early industrial centers in India, particularly around coal mines and textile mills, experienced localized pollution. Post-independence, rapid industrialization, often with inadequate environmental safeguards, coupled with an explosion in vehicular traffic and population density in urban centers, exacerbated the problem.

Major episodic events, such as the severe smog spikes in Delhi during 2016-2021, particularly during the winter months, brought the issue into sharp national and international focus, often linked to seasonal stubble-burning events in neighboring states.

2. Constitutional and Legal Basis

The Indian Constitution, while not explicitly mentioning the 'right to clean air', provides a robust framework through judicial interpretation and legislative mandates:

Article 21 (Right to Life and Personal Liberty): — The Supreme Court of India has consistently interpreted Article 21 to include the right to a clean and healthy environment, encompassing the right to clean air. Landmark judgments have affirmed that pollution-free air is integral to the dignity of life. This makes air pollution a fundamental rights issue, allowing citizens to seek judicial redress.
Article 48A (Directive Principles of State Policy): — This DPSP directs the State to 'endeavour to protect and improve the environment and to safeguard the forests and wildlife of the country'. It serves as a guiding principle for environmental legislation and policy formulation.
Article 51A(g) (Fundamental Duties): — This duty enjoins every citizen 'to protect and improve the natural environment including forests, lakes, rivers and wild life, and to have compassion for living creatures'. It underscores a civic responsibility towards environmental preservation.

Key Legal Frameworks:

Air (Prevention and Control of Pollution) Act, 1981: — This is the primary legislation for air quality management. It established Central and State Pollution Control Boards (CPCB and SPCBs) to prevent, control, and abate air pollution. It empowers these boards to lay down standards, inspect industrial units, and issue directions.
Environment (Protection) Act, 1986 (EPA): — Enacted in the wake of the Bhopal Gas Tragedy, the EPA is an umbrella legislation providing broad powers to the Central Government to take measures for environmental protection and improvement. It allows the government to set national standards for ambient air quality, emissions, and effluent discharge.
Motor Vehicles Act, 1988 (amended): — This Act, along with its subsequent amendments, provides for emission standards for vehicles, mandatory pollution under control (PUC) certificates, and regulations for vehicle maintenance.
Bharat Stage (BS) Emission Norms: — India adopted European emission standards, known as Bharat Stage (BS) norms, to regulate air pollutants from internal combustion engines. The transition to BS-VI norms in April 2020 was a significant leap, mandating cleaner fuels and advanced emission control technologies in vehicles.

3. Key Pollutants, Measurement, and Health Thresholds

Understanding the specific pollutants is crucial:

Particulate Matter (PM2.5 & PM10): — Tiny solid or liquid particles suspended in the air. PM2.5 (diameter < 2.5 micrometers) is particularly hazardous as it can penetrate deep into the lungs and enter the bloodstream. PM10 (diameter < 10 micrometers) includes dust, pollen, and mold. Measurement units are micrograms per cubic meter (µg/m³). WHO annual mean guideline for PM2.5 is 5 µg/m³ and for PM10 is 15 µg/m³. India's National Ambient Air Quality Standards (NAAQS) are significantly higher (40 µg/m³ for PM2.5 and 60 µg/m³ for PM10 annual mean).
Sulfur Dioxide (SO2): — A colorless gas with a pungent odor, primarily from burning fossil fuels (coal, oil) in power plants and industries. Contributes to acid rain and respiratory illnesses. NAAQS: 50 µg/m³ (annual mean).
Nitrogen Dioxide (NO2): — A reddish-brown gas, mainly from vehicular exhaust and industrial combustion. Contributes to smog, acid rain, and respiratory issues. NAAQS: 40 µg/m³ (annual mean).
Carbon Monoxide (CO): — A colorless, odorless gas from incomplete combustion of carbon-containing fuels. Reduces oxygen delivery to organs. NAAQS: 2 mg/m³ (8-hour average).
Ozone (O3) (Ground-level): — A secondary pollutant formed by reactions between NO2 and Volatile Organic Compounds (VOCs) in sunlight. Harmful to respiratory systems and vegetation. NAAQS: 100 µg/m³ (8-hour average).
Ammonia (NH3): — A colorless gas with a sharp odor, mainly from agricultural activities (fertilizers) and waste decomposition. Contributes to secondary PM formation. NAAQS: 100 µg/m³ (annual mean).
Lead (Pb): — A heavy metal, historically from leaded petrol. Now primarily from industrial sources (batteries, smelting). Neurotoxic. NAAQS: 0.5 µg/m³ (annual mean).

Air Quality Index (AQI): India's AQI uses these 8 pollutants. It provides a single number and color for easy understanding. The highest sub-index value for a pollutant determines the overall AQI. (Refer to the AQI table in the revision section for categories).

4. Atmospheric Chemistry and Dispersion

Urban air pollution is not just about direct emissions. Atmospheric processes play a crucial role:

Formation of Secondary PM and Ozone: — Secondary particulate matter forms when gaseous pollutants (like SO2, NO2, NH3, VOCs) react in the atmosphere to create new particles or condense onto existing ones. Ground-level ozone is a classic secondary pollutant, formed photochemically from NO2 and VOCs in the presence of sunlight. These reactions are complex and influenced by temperature, humidity, and solar radiation.
Pollution Dispersion and Mixing Height: — Dispersion refers to the spreading of pollutants in the atmosphere, reducing their concentration. Mixing height is the height of the atmospheric layer near the ground where pollutants are mixed by turbulence. A lower mixing height, common during winter mornings, traps pollutants closer to the ground, leading to higher concentrations.
Inversion Layers: — A temperature inversion occurs when a layer of warm air sits above a layer of cooler air, preventing vertical mixing. This acts like a lid, trapping pollutants beneath it, exacerbating smog events, particularly in winter in North India.
Gaussian Plume and Box Models (Conceptual): — These are simplified mathematical models used to estimate pollutant concentrations. Gaussian plume models predict concentrations downwind from a continuous point source (like a smokestack), assuming a normal distribution of pollutants. Box models treat an urban area as a well-mixed box, estimating average concentrations based on emissions, volume, and removal rates. While complex in detail, understanding their conceptual basis helps appreciate pollution forecasting.
Source Apportionment Techniques: — These scientific methods (e.g., receptor modeling, emission inventories) identify the contribution of different sources (vehicles, industry, biomass burning) to ambient air pollution. This is critical for targeted policy interventions.
Epidemiological Exposure-Response Mechanisms: — Studies link exposure to specific pollutants with health outcomes. For instance, long-term exposure to PM2.5 is linked to increased risk of cardiovascular diseases, strokes, and lung cancer. These mechanisms inform health thresholds and policy targets.
DALYs and Attributable Mortality Estimation: — Disability-Adjusted Life Years (DALYs) measure the total burden of disease, expressed as the number of years lost due to ill-health, disability, or early death. Attributable mortality estimates quantify the number of deaths caused by specific risk factors like air pollution. These metrics, often used by WHO and global burden of disease studies, highlight the severe public health cost of air pollution in India.

5. City Profiles: A Snapshot of Urban Air Quality

Indian cities face unique pollution challenges, often influenced by geography, meteorology, and local economic activities. Recent PM2.5 annual averages (latest available year, e.g., 2023 data from various reports) consistently show levels far exceeding WHO guidelines.

Delhi (NCR): — Consistently among the world's most polluted. Typical seasonal pattern: severe smog in winter (October-February) due to inversion, low wind speeds, and stubble burning. Dominant sources: vehicular emissions (estimated 20-40%), industrial pollution, construction dust, domestic biomass burning, and regional sources like stubble burning. Recent PM2.5 annual average: often 80-100 µg/m³ (WHO guideline 5 µg/m³). Notable events: Odd-Even scheme implementation, Graded Response Action Plan (GRAP) activations, Supreme Court/NGT interventions. is a critical node here.
Mumbai: — Coastal city, pollution often exacerbated by sea breeze inversions. Dominant sources: vehicular, industrial (refineries, power plants), construction, waste burning. Recent PM2.5 annual average: 40-60 µg/m³. Notable events: increasing winter pollution, construction boom impacts.
Kolkata: — High population density, old vehicle fleet, industrial belt. Dominant sources: vehicular, industrial, domestic fuel, waste burning. Recent PM2.5 annual average: 60-80 µg/m³. Notable events: persistent winter smog.
Chennai: — Coastal city, relatively better air quality than northern counterparts but still exceeding standards. Dominant sources: vehicular, industrial (petrochemicals, power plants), dust. Recent PM2.5 annual average: 30-40 µg/m³.
Bengaluru: — Rapid urbanization, vehicular congestion. Dominant sources: vehicular, construction, industrial. Recent PM2.5 annual average: 35-50 µg/m³. Notable events: traffic-induced pollution spikes.
Hyderabad: — Growing IT hub, increasing vehicular load. Dominant sources: vehicular, industrial, construction. Recent PM2.5 annual average: 35-50 µg/m³.

6. Sources and Contributions

Source apportionment studies reveal varying contributions across cities and seasons. While the prompt references 50% for vehicular emissions, official estimates often show a range, and it's crucial to acknowledge this variability. For instance, CPCB reports and studies by institutions like TERI or IIT Kanpur indicate:

Vehicular Emissions: — A major contributor, often ranging from 20-40% of PM2.5 in large metropolitan areas like Delhi, though some older estimates placed it higher. The prompt's reference to 50% highlights its significant impact. Key pollutants: PM, NOX, CO, VOCs. Implementation of BS-VI norms is a significant step.
Industrial Emissions: — Power plants (especially coal-fired), brick kilns, small-scale industries, and manufacturing units contribute significantly (15-30%). Pollutants: SO2, NOX, PM.
Construction and Demolition Dust: — A ubiquitous source in rapidly developing cities (10-20%). Uncontrolled dust from building sites, roads, and infrastructure projects.
Crop Residue Burning (Stubble Burning): — Predominantly in North India (Punjab, Haryana, UP) during post-monsoon (October-November), contributing up to 30-40% of Delhi's winter pollution on peak days. Releases PM, CO, VOCs, and black carbon. on environmental movements often highlights local resistance to such practices.
Thermal Power Plants: — Significant regional contributors, especially those located near urban centers. Emit SO2, NOX, and PM. Strict emission norms are being phased in.
Municipal Waste Burning: — Open burning of solid waste in urban and peri-urban areas (5-10%). Releases toxic gases, dioxins, furans, and PM. on solid waste management is directly linked here.
Domestic Fuel Burning (Biomass): — Especially in peri-urban and slum areas, burning wood, dung cakes, and coal for cooking and heating (5-15%). Major source of indoor and outdoor PM.

7. Policy Timeline and Recent Developments

1974: — Water (Prevention and Control of Pollution) Act (precursor to CPCB).
1981: — Air (Prevention and Control of Pollution) Act enacted, establishing CPCB and SPCBs.
1986: — Environment (Protection) Act enacted, providing comprehensive powers.
1990s-2000s: — Introduction of emission norms for vehicles (Bharat Stage norms), mandatory PUC certificates, CNG conversion in Delhi.
2016-2021: — Recurring severe smog episodes in Delhi NCR, leading to emergency measures like GRAP and Odd-Even schemes.
2019: — Launch of National Clean Air Programme (NCAP), aiming to reduce PM2.5 and PM10 concentrations by 20-30% by 2024 (with 2017 as the base year) in 132 non-attainment cities. It's a long-term, time-bound national-level strategy.
2020: — Implementation of BS-VI emission norms nationwide from April 1. This was a significant technological leap for vehicular emissions.
2020: — Formation of the Commission for Air Quality Management (CAQM) in NCR and Adjoining Areas, replacing the EPCA. CAQM is a statutory body with overarching powers to coordinate efforts, research, and enforce measures for air quality improvement in the region.
Recent Developments (2024-2026): — Ongoing evaluation of NCAP targets, discussions on extending targets beyond 2024, stricter enforcement by CAQM, focus on green hydrogen and electric vehicles, and international collaborations (e.g., discussions at COP28 on reducing non-CO2 greenhouse gases and air pollutants). WHO's updated Global Air Quality Guidelines (2021) set much stricter limits, highlighting the gap India needs to bridge.

8. Vyyuha Analysis: Challenges and Way Forward

The air pollution crisis in Indian cities is a complex adaptive challenge, requiring integrated solutions. Vyyuha's analytical lens reveals several critical aspects:

Governance Failure and Coordination Deficits: — Despite numerous laws and bodies, effective implementation and inter-agency coordination remain weak. The problem transcends administrative boundaries (e.g., stubble burning affecting Delhi), necessitating robust federal-state coordination. CAQM is a step in this direction for NCR, but similar mechanisms are needed elsewhere.
Political Economy of Pollution: — Economic growth often takes precedence over environmental protection. Industries resist stricter norms due to cost implications. The informal sector, a significant polluter, is difficult to regulate. Subsidies on polluting fuels or technologies can create perverse incentives.
Role of Judiciary: — The Supreme Court and National Green Tribunal (NGT) have played a proactive role, issuing landmark judgments (e.g., MC Mehta v. Union of India on various environmental issues, Vardhaman Kaushik v. Union of India leading to GRAP) and orders on stubble burning, vehicular pollution, and waste management. However, judicial activism needs to be complemented by executive action.
Data Gaps and Monitoring: — While monitoring networks have expanded, granular, real-time data for all sources and locations, especially in smaller cities, is still lacking. Accurate source apportionment is crucial for effective policy.
Public Awareness and Participation: — While awareness is growing, public participation in pollution control efforts (e.g., waste segregation, public transport use) needs to be enhanced. Behavioral change is a critical, yet often overlooked, component.

9. Inter-Topic Connections (Vyyuha Connect)

Air pollution is not an isolated issue; it is deeply intertwined with other environmental and developmental challenges:

Sustainable Development Goals (SDGs): — Directly impacts SDG 3 (Good Health and Well-being), SDG 11 (Sustainable Cities and Communities), and SDG 13 (Climate Action). Reducing air pollution contributes to achieving multiple SDGs.
Urban Planning: — Congested cities, inadequate public transport, lack of green spaces, and poor waste management contribute to pollution. Integrated urban planning, promoting compact, mixed-use development and green infrastructure, is essential.
Public Health: — Air pollution is a leading cause of premature deaths and morbidity in India. It strains public health infrastructure and increases healthcare costs. on industrial disasters also highlights health impacts.
Climate Change: — Many air pollutants (e.g., black carbon, methane, ground-level ozone) are also short-lived climate pollutants (SLCPs). Reducing them offers a 'win-win' solution, improving air quality and mitigating climate change. on climate change mitigation strategies is highly relevant.
Energy Transition: — Reliance on fossil fuels for power and transport is a major source. Transition to renewable energy and electric vehicles is critical for long-term solutions.
Waste Management: — Open burning of municipal solid waste is a significant source of urban air pollution. Effective solid waste management is crucial.
Water Pollution: — While distinct, environmental governance failures often manifest across sectors. on water pollution crisis shares common underlying issues of regulatory enforcement and public awareness.
Coastal Pollution: — on coastal pollution and marine ecosystem degradation also highlights the interconnectedness of environmental challenges and the need for holistic policy approaches.

Authoritative References:

1
Central Pollution Control Board (CPCB) Annual Reports on Air Quality.
2
Ministry of Environment, Forest and Climate Change (MoEFCC) Notifications and Policy Documents.
3
World Health Organization (WHO) Global Air Quality Guidelines (2021).
4
Supreme Court of India Judgments (e.g., M.C. Mehta v. Union of India, Vardhaman Kaushik v. Union of India).
5
Reports by institutions like TERI, Centre for Science and Environment (CSE), IIT Kanpur on source apportionment.
6
Commission for Air Quality Management (CAQM) in NCR and Adjoining Areas - Annual Reports and Directions.
7
The Lancet Planetary Health - Global Burden of Disease studies on air pollution.
8
NITI Aayog reports on sustainable development and environmental policy.

Often confused with

Side-by-side differences the UPSC paper likes to test.

Air Pollution in Indian Cities vs Primary Pollutants vs. Secondary Pollutants

Aspect	Air Pollution in Indian Cities	Primary Pollutants vs. Secondary Pollutants
Definition	Emitted directly from a source into the atmosphere.	Formed in the atmosphere through chemical reactions between primary pollutants or with other atmospheric constituents.
Origin	Direct emission from anthropogenic (e.g., vehicle exhaust, industrial stacks) or natural sources (e.g., volcanic eruptions, dust storms).	Result of atmospheric chemical processes, often involving sunlight (photochemical reactions).
Examples	Carbon Monoxide (CO), Sulfur Dioxide (SO2), Nitrogen Oxides (NOx) from combustion, Particulate Matter (PM) from dust/soot, Lead (Pb).	Ground-level Ozone (O3), Peroxyacetyl Nitrate (PAN), secondary Particulate Matter (e.g., sulfates, nitrates formed from SO2 and NOx).
Control Strategy	Focus on source reduction (e.g., emission controls, cleaner fuels, industrial filters).	Requires controlling precursor primary pollutants and understanding atmospheric chemistry (e.g., reducing NOx and VOCs to control ozone).
Visibility	Can be visible (e.g., smoke, dust) or invisible (e.g., CO).	Often contribute to haze and smog, reducing visibility (e.g., secondary PM, ozone).

Understanding the distinction between primary and secondary pollutants is fundamental to devising effective air pollution control strategies. Primary pollutants require direct emission control at the source, whereas secondary pollutants necessitate a more complex approach involving the reduction of their precursor gases and an understanding of atmospheric chemistry.

For instance, controlling ground-level ozone requires tackling both nitrogen oxides and volatile organic compounds, not just one. This differentiation guides policy interventions, from vehicular emission standards to industrial stack controls and regional air quality management plans.

Why it is tested: Crucial for Prelims (identifying pollutant types) and Mains (designing effective pollution control strategies, understanding atmospheric processes, and source apportionment). Helps in analyzing the complexity of urban air pollution.

Air Pollution in Indian Cities vs National Clean Air Programme (NCAP) vs. Graded Response Action Plan (GRAP)

Aspect	Air Pollution in Indian Cities	National Clean Air Programme (NCAP) vs. Graded Response Action Plan (GRAP)
Objective	Long-term, time-bound national strategy to reduce overall particulate matter concentrations.	Emergency, short-term measures to be implemented based on the severity of air quality in Delhi-NCR.
Scope	Covers 132 non-attainment cities across India.	Primarily focused on Delhi-NCR, though the concept can be adapted elsewhere.
Time Horizon	Long-term (5-year target, with potential extensions), aiming for sustained improvement.	Short-term, reactive, triggered by specific AQI thresholds to prevent further deterioration.
Measures	Includes source-specific interventions, strengthening monitoring, public awareness, capacity building, and technological solutions.	Specific actions like banning construction, restricting vehicular movement (Odd-Even), shutting down polluting industries, banning diesel generators.
Trigger	No specific trigger; it's an ongoing program based on historical pollution levels.	Triggered by real-time AQI levels (e.g., 'Poor', 'Very Poor', 'Severe', 'Severe Plus').
Implementing Authority	Ministry of Environment, Forest and Climate Change (MoEFCC) through CPCB and State Pollution Control Boards.	Commission for Air Quality Management (CAQM) in NCR, based on CPCB's recommendations, with enforcement by local bodies.

NCAP and GRAP represent two distinct yet complementary approaches to air pollution control in India. NCAP is a strategic, long-term framework aimed at achieving sustained reductions in pollution levels across multiple cities through a range of systemic interventions.

In contrast, GRAP is a tactical, emergency response mechanism specifically designed for Delhi-NCR to mitigate severe pollution episodes by implementing stringent, short-term measures. While NCAP seeks to address the root causes and achieve gradual improvement, GRAP acts as a critical safety net during acute pollution crises.

Both are vital for comprehensive air quality management.

Why it is tested: Essential for Prelims (identifying objectives and scope) and Mains (evaluating policy effectiveness, comparing different governance mechanisms, and analyzing the multi-pronged strategy needed for air pollution control). Helps in structuring answers on policy responses.

Questions students ask

8 answered on this topic.

What is the Air Quality Index (AQI) and how is it calculated in India?

The AQI is a tool to communicate air quality status to the public in a simple, understandable manner. In India, it is calculated based on eight major pollutants: PM2.5, PM10, NO2, SO2, CO, O3, NH3, and Pb. For each pollutant, a sub-index is calculated based on its concentration and a predefined health breakpoint. The overall AQI for a location is the maximum of these sub-indices, representing the pollutant with the highest health risk. It is color-coded and categorized from 'Good' to 'Severe'.

Which Indian cities have the worst air pollution levels?

Historically, cities in the Indo-Gangetic Plain, particularly Delhi and its surrounding National Capital Region (NCR), have consistently ranked among the most polluted globally. Other major cities like Kolkata, Lucknow, Kanpur, and Patna also frequently experience very poor to severe air quality, especially during the winter months.

While coastal cities like Chennai and Bengaluru generally have better air quality, they still exceed national and international standards at times, primarily due to vehicular and industrial emissions.

What are the main sources of air pollution in Delhi?

Delhi's air pollution is a complex mix of local and regional sources. Major local contributors include vehicular emissions (a significant share, often 20-40%), industrial pollution (from surrounding NCR areas), construction and road dust, and domestic biomass burning.

Regional sources, particularly crop residue burning in Punjab and Haryana during winter, significantly exacerbate the problem, contributing to severe smog episodes. Meteorological factors like low wind speed and temperature inversions also play a crucial role in trapping pollutants.

How effective is the National Clean Air Programme (NCAP)?

The NCAP, launched in 2019, aims to reduce PM2.5 and PM10 concentrations by 20-30% by 2024 in 132 non-attainment cities. While some cities have shown marginal improvements, overall progress has been mixed.

Challenges include inadequate funding, lack of robust source apportionment studies for all cities, weak enforcement mechanisms, and insufficient inter-agency coordination. Its effectiveness is still under evaluation, and there's a recognized need for more aggressive and targeted interventions to meet its ambitious goals.

What are the health effects of PM2.5 and PM10 exposure?

Both PM2.5 and PM10 are inhalable particulate matter, but PM2.5 is more dangerous due to its smaller size, allowing it to penetrate deeper into the lungs and even enter the bloodstream. Exposure to these pollutants can lead to a range of health issues, including respiratory problems (asthma, bronchitis), cardiovascular diseases (heart attacks, strokes), lung cancer, and premature mortality.

Vulnerable populations like children, the elderly, and those with pre-existing conditions are particularly at risk.

How does stubble burning contribute to North India's air pollution?

Stubble burning, the practice of setting fire to crop residue after harvest, primarily in Punjab, Haryana, and parts of Uttar Pradesh, is a major seasonal contributor to air pollution in North India. The smoke, laden with particulate matter (PM2.

5, PM10), carbon monoxide, and other harmful gases, travels downwind, significantly impacting air quality in Delhi-NCR and other cities during October-November. It exacerbates winter smog, leading to severe health hazards and reduced visibility.

Efforts are ongoing to promote in-situ and ex-situ management alternatives.

What Supreme Court orders have been passed on air pollution?

The Supreme Court has passed several landmark orders. Key among them are the M.C. Mehta cases, which led to the conversion of Delhi's public transport to CNG, relocation of polluting industries, and the establishment of environmental authorities.

The Vardhaman Kaushik case led to the formulation of the Graded Response Action Plan (GRAP) for Delhi-NCR. The Court has also issued directives on vehicular emission norms (e.g., BS-VI implementation), waste management, and stubble burning, consistently upholding the right to a clean environment under Article 21.

Which emission standards apply to vehicles in India?

Vehicles in India are subject to Bharat Stage (BS) emission norms, which are based on European standards. India transitioned directly from BS-IV to BS-VI norms nationwide from April 1, 2020. BS-VI standards are significantly stricter, mandating lower limits for pollutants like nitrogen oxides (NOx), particulate matter (PM), and sulfur content in fuel.

This requires advanced emission control technologies in vehicles, such as Diesel Particulate Filters (DPF) and Selective Catalytic Reduction (SCR) systems, aiming for cleaner vehicular emissions.